1. Field of the Invention
The present invention relates to an electromagnetic shield plate.
2. Description of the Related Art
Electromagnetic shield plates have been used widely as front panels to be mounted in front of display screens to provide, for example, a shield from electromagnetic radiation leaking from the front side of the display. Electromagnetic shield plates used as the front panels are required not to degrade the visibility of the display screen, while providing the function of shielding electromagnetic radiation.
One known type of such electromagnetic shield plates is constructed, for example, by bonding an electrically conductive mesh to a substrate. The conductive mesh is formed by weaving an electrically conductive fiber in a grid pattern; for example, a polyester fiber or the like whose surface is coated with a metallic thin film is used as the electrically conductive fiber.
However, electromagnetic shield plates using such a conductive mesh have had the problem that the conductive mesh that has to be used in the fabrication process is a fabric which is likely to expand and contract during the fabrication and is therefore not easy to handle. Furthermore, when using the electromagnetic shield as a front panel, its transmittance of light in the visible spectrum must be increased, and to achieve this, the grid interval of the conductive mesh must be increased and the fiber diameter be reduced, making it imperative to use a conductive mesh more prone to expanding and contracting and hence more difficult to handle. This has involved the further problem that the grid interval tends to become displaced and distortion of the grid pattern tends to occur when bonding such an easily expanding and contracting conductive mesh to the substrate.
One possible solution to such problems may be to use an electromagnetic shield plate constructed with an etching sheet formed by etching a metallic foil in a grid pattern and bonded to the surface of the substrate; however, if the front panel is to be usedwith a large-screen display such as a plasma display or a large-size CRT, a large-area metallic foil that matches the screen size must be etched in a grid pattern. This necessitates the use of a large-scale photolithographic process, and it cannot be said that such shield plates are easy to fabricate.
On the other hand, there has been proposed an electromagnetic :shield plate constructed by printing an electrically conductive paint in a grid pattern or a stripe pattern (Japanese Unexamined Patent Publication Nos. 62-57297 and 02-52499), but this electromagnetic shield plate has a grid interval of 1000 xcexcm and a line width of 100 xcexcm and does not necessarily provide sufficient electromagnetic shielding properties; furthermore, visibility is also insufficient because the grid lines tend to be visible.
In view of the above situation, the present inventors have conducted intensive studies to develop an electromagnetic shield plate that is easy to fabricate even in large size and that provides excellent visibility and electromagnetic shielding properties, and found that an electromagnetic shield plate that is easy to fabricate even in large size and that provides excellent visibility and electromagnetic shielding properties can be obtained by forming a geometric pattern having a line width of 10 xcexcm to 80 xcexcm and a line interval of 50 to 250 mesh on a transparent substrate surface by the use of a printing method, and this finding has lead to the present invention.
Accordingly, an object of the present invention is to provide an electromagnetic shield plate comprising a geometric pattern having a line width of 10 xcexcm to 80 xcexcm and a line interval of 50 to 250 mesh on a surface of a transparent substrate.